Apparatus for screening pulp



April 1942- A. D. MERRILL 2,278,729

APPARATUS, FOR SCREENING PULP Filed Dec. 2, 1937 2 S heets-Sheet 1awe/who'l flat/era Maze/2.4

April 7,' 1942.

A. 0.] MERRILL APPARATUS FOR SCREENING PULP Filed Dec. 2, 1957 2Sheets-Sheet 2 gjwuwrvtom v 3 Hazard/7:04am W7 Patented Apr. 7, 1942 I 7"UNITED STATES PATENT OFF-ICE APPARATUS FOR scaaanmo. PULP Albert n.Merrill, Water-town, N.- Y, Application December 2, 1931, Serial No.177,195

1 Claim. ((1192-32) This invention relates to pulping apparatus,moreparticularly to an improved apparatus for screening of pulp, I

A typical pulp screening apparatus, employed at the present time,comprises a screen member on which the stock to be filtered or screenedis fed and below which a flexible diaphragm is positioned. The diaphragmis associated with mechanical means to efiect its vibration. In use thepulp which is to be screened is forced or ,drawn through the screenplates by the pulsating movement of the body of pulp or liquid, estab.-

lished by the vibratory movement of the diaphragm. The body of liquid isnormally main- 'tained at a predetermined levelby utilizing an outletseal so that a suitable depth of the stock is maintained over thediaphragm. ,In the operation of this type of structure, the pulsatingmovement of the, body of liquid causes the finer fibers to be forced or,sucked throughthe' interstices in the screen while withholding orscreening out the larger particles.

In the past, a number of different methods of efiecting the vibrationofthe diaphragm have been'proposed. Amonglsuch methods is the socalledpositive drive that is to say adrivlng mechanism which is connected tothe. resilient" diaphragm so that theidiaphragm is positively movedineach direction of its reciprocating motion. 7 t

the screen, as is known, are quite small. When the diaphragm is given apositive upward stroke by means of a non-resilient connecting rod, thebody of liquid similarly tends to pulsate upwardsimple and efficaciousmethod-of preventing such l breakage, but also to a methodof increasingThe present invention relatesx not only to a production of'a screeningapparatus. The broad concept ofthepresent niethod'involves theelimination of such breakage by providing a special type of outlet suchthat the liquid below the screen may be caused to flow outwardly of thescreenon each reciprocation'ot the diaphragm. thus relieving theundesired dangerous pressure.

tion, as will be seen, the operation increases the production by reasonofan increased; flow of stock through the device. ',An additional andnovel feature ofjtheinvention-is effectually -to adapt the screeningunit to difierent types of fiber stock'- so as to correlate the speedofthe ular characteristics of that stock.

discharge of stock with respect to the partic- With this fundamentalconcept-in view, it will be appreciatedthat'a'ziumberbfldifierent'speciflc'mechanical structuresmay-belutilized to V the accompanying 7 drawings, inwhich:

1y. In some circumstances, the fibers may clog the interstices in thescreen, thus establishing a hydraulic hammer or rain; In other words.

when the interstices of the screen areplugged,

the upwardly moving body of liquid is suddenly arrested and aconsiderablepercussive pressure-- is. applied to the screen inconsequence of the upward momentum of the'liquid magmas In manycircumstances, this is of such a magnitude Figure l'is'a transversesection oi a pulp screen according to the invention;

of construction.

Figure 3 is a similar view of another modification of the invention. V

Figure 4 is a detailed view illustrating the 7 Figure 2 is a similarview of a modified form 'utilization of a' positively controlled flow of:screened pulp in the type of apparatus shown inFiguresland 2. V 5Figures 5 and 6 illustrate, similarly, methods of positively controllingthe new irom 'screen boxes 01' the type shown in Figure 3.

As shown in the drawings, a series of slotted screen Plates I aresupported in a traminf dicated generally at 2, which framing serves as acontainer for the pulp to be "treatedJA dia- The screen is suitablysecured to the framing in any desired manner, as for example by beinglocked between the shoulders 2' and the removable plate fasteningi'rames4. Obviously, any

enmmmmaa tcumu us o yard;

metal plate i ,on which is formedan apertured shoulder I to which theconnecting rod I is pivotally connected. At its other end the connectingrod is associated with any suitable mech which functions to impart apredetermined reciprocating motion to the .eonnectins rod and thence tothe diaphragm.- ,-Such connection is shown as comprising the driving e.t6 themain'drive'shait:

imlconmneri-aibmmed use man with a passageway or duct l i, thrcugh whichscreenedstockpasses to thetroughdi. As will l which is keyed screenedstock .by those 'skilledjin th'eart,lthe passes fromthetrough I! throughusual outlet seal (not shown'i, which is operative to maintains body.ofthe liquid pulp at a predetermined depth in screening; chamber..It'wlll be understood that, in the operation of suchmeehanism, thevibratory movement of .the diaphragmstransmits a correspondingpulsatingmovement to the liquid mass in the-screen- ;ing" This pulsatingmovement at the :one time tends. to draw the liquid and the finer Jlbersthrough the screen apertures, and by rea- "of the agitation. due topulsaticn in the liquid body, to prevent immediate 1-1odgment in thescreen apertures. ,In actual-practice, however. itjis-found that 1-2 gPulp which. under the action of the diaphragm,

.someffibersyattach to. the sides 'oithe apertures,

or slots; in thefplates. and tend .progressivelyjtog stroke oi thediaphragm. In other words, on the downstroke of the diaphragm, the nowof the suspended finer particles down through the screen is induced. Onthe up-stroke of thediaphragm, since the pressure oi the liquid adjacentthe screen increases considerably above that in the sealing tube il, apredetermined amount of the screened pulp flows outwardly through thetube. This now of' liquid obviously relieves the impact pressure on thebottom of the screen and thus eliminates the possibility of'suchpressure building up to the danger point, that is, to the extent orbreaking the screen plate.

It will also be seen that this type of operation considerably increasesthe output of the machine, as well as serving to clean the screen. Aswill be observed {mm the figures, the flow of liquid through theauxiliary outlet 2| tends to be substantially parallel the bottom'of thescreen, in contradistinctionto the main movement of the is substantiallyvertical or reciprocatory. In these thereiore,'the flow of liquid h ou htube :0 tends to shear away fibers which may have adhered to theunderside of the screen. It will also be appreciated that; in the oldertype of structure, under the pulsating action of the diaphragmron theup-stroke, -a consider-,

able amount of liquid was forced upwardly through the screen aperturesand effective now of pulp through the machine was dependent largely onthe down. or suction stroke of "the diaphragm. In the present type orstructure,

however, the diaphragm incombination with the two outlets II and 2|functions essentially as'a' double acting pump. 0n thedown-stroke,'liquid is drawn through the screen and overflows into thetrough to be discharged in the usual man,-

her. On the upstrokefas explained, not an inconsiderable quantityof thepulp is forced outwai'dly through the seal 20. It will thus be observedthat the output from this type of machine 7 veis iz'eoftheaperturesandultimatelyblocking f 5 r vi us y explained the ll itself1 ynence; when the screen I p a-certain;point,-the-upl V .ffi ifl fnqid-body issuddenlyf;

thereby -applyinrapressure or con--" 1 magnitude underside ,ofthev'iewof' large of :the liquid,j.=this percussive force may reach such I,Ea magnitude {as to fracture the screen.

i sa w er in ention,.; such danger oi breaking the screen is' This isdone by providing 1 the principles-of the present ""ai seri'essoi:safety outlets for the liquid and-prefof this potential water-vhammeractlon, that is to say, adjacent the undersidefroflthescreen.shown imfigure 1," thisben'eiicial result may. be achieved by the.

simpleexpedient or empioyinaxa seal outletjadjacent the'underside of theplate. Such'outlet .may comprise the-usual form of suchasthernemberll.v

Ll-tube seal, It will be seen that sums structure establishes a newmode. of operation for the screening devicein that it provides for whatin function may is 'considerabiy greater than from one which isnot'soconstrucied.

It will'readilybe understood'that, with the broad concept in mind, anumber of specifically different types of'structures may be provided,particularly in 0,1 the typ of seal used.

An example of such alternative construction is shownin Figure 2, inwhich the special double bend seal- I. is employed. As will have beenappreciated this sealfunctions essentially in the same manner as sealII, shown ingFigure 1.

Since the essential offthe seal is that iof a valve, allowingamaintenance of suction on the" down str'oke; and an outward flowof'pulp on -theupstrokeit is clear that other ".*types may beused. Theauxilia y outlet t fore, need' notbe a seal of the typelshown, but

may be of any other typeof structure in which these essential functionsare performed. In the 'type of structure shown, the size of the seal 2|for SI' will, oicour'se, depend uponthe relative of the screeningchamber, the depth of the ,stock; the-speed of vibrationfof the"diaphragm, .andthe like. 'lln typical installations, .such a 'seal maybe of the order 0! from 2 to18 inches. inany'. ev'ent, [as explainedptheseal'is so conbe considered a check valve, allowing a now of -theliquidfrom-the area subiacent the screen,

under, predetermined pressure-conditions, and

preventing;this now imder certain different pressure conditions. Duringoperation, it will be undersmod that. the outlet tube il'iss'ealed andhence does not break the suction on the downstream, to insure amaintenance of the suction orvacuum on the ldown stroke and a positiveoutward now of liquidjontbe upstroke, thus preventing the application]of anyconsiderable impact pressure on the screen.

Sincea' salient feature of the invention'is the establishment of aoutward flow of screened stock on each stroke of the diaphragmwhile-insuring the effective suction of the downstroke, it will beappreciated that this may be accomplished by other methods. The deviceillustrated in Figures l and 2 show, ineflfect, the

achievementof this new functionin an existing type of machine having theusual low level discharge (I I). In such a structure the benefits of thinvention may be secured by providing a secondary or auxiliary outlet 20(Figure. 1) or III (Figure '2). The same essential functionsmay be.secured by constructing a screening device having a special singleoutlet such as is shown inv FigureB. In such anapparatus, asindicated,the construction of the screen box and the relative location of thescreenand diaphragm may be the same as that shown in Figures 1 and 2,

and such have therefore been indicated by identical numerals. Under theinvention as shown in Figure 3 a special type of single outlet 40 isprovided. As shown this comprises a' substantially U-shaped portion 4|,constructed in a manner similar to that of the sealing discharge units20 and 30 shown in Figures 1 and 2 respectively. Such a U-shapeddischarge duct .serves to permit outward flow of the screened stockunder predetermined hydrostatic pressure conditions and also acts as aseal to maintain the desired suction in the screening chamber. As willbe noted from an inspection of Figure 3,

.the discharge tube 40 is connected to the screen box and is thereforein fluid communication with the mass of pulp in the box at relativelyhigh point and closely subjacent the screen. In these circumstances, thedischarge tube perform the functicn'of both'the low level discharge IIand the discharge. tube 20 and 30 of the structure shownin Figures 1and}. I

In operation, when the diaphragm 3 is vibrated under the action of thedriving mechanism 8-40,

the screen stock is caused to flow outwardly through the tube '40 oneach-stroke of the diaphragm. Due to the utilization of the U-tubesection and, hence, the establishment of a liquid seal, the desirablesuction on the down-stroke of the diaphragm is maintained. 0n theupstroke of the diaphragm the screened stock is caused to flow outwardlythrough the U-tube when the pressure obtaining in the body of pulpexceeds that established by the particular height- 013 the seal, whichis chosen. In this type of structure, therefore, in accordance with thegeneral principles of the invention, the double pump action is secured,a greater 'thruput of stock is achieved;

andthe undesirable hydraulic hammer efiect the bottom of the screen'isprecluded.

As is known to those skilled in the art, a particular pulp mill mayoperate upon different types of cellulosic stock and may, in the courseofits normal operations, cook materials varying from a very soft to avery hard stock. It has been found that the flow of the pulp through aparticular screening apparatus is greatly influenced by the particularcharacteristics of .the stock and, as a matter of fact, such flow is. inpart a function of such characteristic of the stock.

According to another feature of theinvention, increased efllci'ency maybe assured by providing means for regulating the discharge of pulp fromthe screening mechanism with respect to the character of the particularstock flowing through it. In these circumstances, the retention periodin the screening device and-the quality of the product can bepredeterminedand maintained.

. rection, the aperture 6| maybe moved :in and out.

of register wtih the discharge duct '41 so as to ablevalv 5 5eflectivejcro'ss sectionaljfsize and hence-the speed ih re i us n w. bontro d- Similar'meansare provided; tocontrol the size of the comprisesthe gacewalve member-50. Ihis'valve =is provided with the aperture 5]and the valve is adapted to slide, in the known manneninthe aperturedguide 52.. At its'upperflportionthe gate is provided withthethreadedstem 53, on

the end of which is 'provided'the usualfoperatm handle. It will beunderstood thatwith this type of structure, by rotating thehandlejon thegate valve 50, the aperture 5| may be moved vertically upwardly anddownwardly so as to control theefiective size of the discharge, and

thus regulate the amount of stock discharged the discharge tubes II and20, respectively.

It will be'appreciated thatthis same type of controlled operation may beutilized with the.

single discharge screen structure of .the type shown in Figure 3. Thus,as shown in Figure 5, the screen may be provided with a gate valve ofthe type shown in Figure 4. This valve may comprise the gate or plateformed with the aperture. :6l. the apertured plate seat 62. The upperportion of the. gate is connected with the threaded stem at the end ofwhich is provided theusual operating handle. In this type 'ofstructure,. by rotating the handle .of the stem- 63 in the properdicontrol the effective size of the discharge tube and henceregulate'the amount ofpulp flowing therethrough.

It will be understood that the invention com prehends broadly thecontrol of flow of the screened pulp outwardly of the screen box.

comprises a gate valve platewhich. has a plurality oforiflces ofpredetermined size; Sucha valve may comprise the gate plate I0, providedwith l the differential size orifices 1|, I2 and .13, respec- Theseadvantages may be secured-by the simple tively. The valve may be mountedfor vertical movement in the valve seat platefl. At the upper 'end thevalve may be provided with an 'apertured handle'or stud 1.5 in which thelatch I6 is adapted to reciprocate. The latch 16, it willbe understood,is adapted to project through the stud I6 and engage in the detents ordepressions 11. Such detents are, in the mafiner known. vto thoseskilled in the art, suitably vertically spaced so that they conform tothe several registe ms position of the apertures ll, 12 and I3.

The gate is adapted to reciprocate in,

4 amazon In the structure shown in Figure 6, for example, the gate valveis set so that the middle sized aperture 12 is in register with thedischarge line ll-Ji. By withdrawing the member I. from register with adetent, the gate Ill may be elevated or depressed, by utilizing the studhandle 15 so as optionally to register apertures II, I! or 18 with thedischarge opening Hi.

The particular types of valves have been given as merely illustrative ofany mechanism which functions in a similar manner to control the flow ofstock through either the single discharge type of screen (Figure 3) orthrough the double type discharge (Figures 1 and 2).

It will be appreciated that the present invention presents a simple andeffective method of eliminating a marked defect in pre-existingprocesses and furthermore insure the positive and additional advantageof a considerably greater thruput of stock, the flow of which mayaccurately be'controlled. While preferred modifications of the inventionhave been described, it is to be understood that these are given'toexemplify the underlying principles involved, andnot as limiting thefundamental concept to the "precise apparatus chosen for illustrativepurposes.

I claim:

A pulp screening apparatus comprising a container, a screen mounted atthe upper part of the container, a resilient diaphragm mounted at thebase of the container, positive driving means for the diaphragm; anoutlet for the container located closely adjacent thescreen, a valve insaid outlet, a second outlet from the container located closely adjacentthe diaphragm, a control valve in said outlet and means to eilfect acontrolled flow of screened pulp through each of said outlets.

' ALBERT D. MERRIIL.

